Fyi . . .

For the fun of it ... I used a Skip Level while I have all levels unlocked just to see what would happen.

And it just used the Skip Level, and didn't pop up any message, no indication of success or failure.

Not sure if this means it vanished into the void, or if additional levels are ever created, that I'll be able to start from the map 2 levels after the USA (b/c I've already unlocked the one directly after b/c I beat USA).

You’ve unlocked the secret cow level. Rename your account “Moooooo” and it will show up.

I’d recommend checking with Fizzer on that one